Building an inversely zoned post-orogenic intrusion in the Neoproterozoic-Cambrian Aracuai orogen (Brazil)

Post-orogenic plutons are excellent recorders of the last stages of collapsing orogens. In the NeoproterozoicCambrian Aracuai orogen (Brazilian Southeast), one of the Brasiliano orogenies (Western Gondwana), voluminous amounts of Cambrian magmatism crop out. The Venda Nova pluton (VN) is located at the southern portion of the AO, exhibiting a norite/charnockitic west-ring in contact with a syenomonzonite that envelops an alkaligabbro core with distinct geochemical signatures. To explore the tectonic significance of this post-orogenic pluton in the AO, anisotropy of magnetic susceptibility (AMS) together with a microstructural analysis were performed. AMS data reveals, majorly, a concentric magnetic foliation/lineation pattern, implying that buoyancy forces controlled the magma emplacement of syenomonzonites and gabbros, while a previous pulse of a charnockitic intrusion was deformed by their intrusion. Restrict solid-state deformation (following the regional trend) inside the pluton could result of the reactivation of an emplacement structure in the last stages of VN crystallization. The emplacement of inversely zoned post-orogenic plutons through deep conduits in the colder forelands of the AO, such as the VN, might record different stages of a large collapsing orogen in a single plutonic body.

Automated summary

By analyzing the anisotropy of magnetic susceptibility and microstructural characteristics, the study reveals the tectonic significance of the Venda Nova pluton in the collapsing orogen, showing that buoyancy forces controlled magma emplacement and solid-state deformation within the pluton may result from reactivation of emplacement structures. The emplacement of inversely zoned post-orogenic plutons in colder forelands of the orogen may record different stages of a large collapsing orogen in a single plutonic body.